Rubber physics in a Hollow World

[fmitchell]

Mostly for my own amusement, I'm working on a science fantasy hollow world campaign. One of the premises is that things that look like magic are really super-science. Therefore, I'm stumped as to how people and things stick to the inner surface of a globe, given that there's no gravity inside a globe.

1. Centripetal force from the hollow world's spin simulates gravity. Unfortunately, gravity will diminish with latitude: 15 degrees off the equator the effect is notable, and by 30 degrees the apparent gravity is about 3/4 the equator. Also, the slope will tend to make things roll toward the equator, since the "centrifugal force" is orthogonal to the direction of spin, not the surface. It might as well be a ringworld, even if I presume the mysterious Builders made the world a prolate spheroid or a cylinder with spherical caps.
   
2. There's some sort of artificial gravity that keeps things on the surface. It's short range, somehow; gravity from opposite points don't cancel it out, and after a certain point it stops working altogether.
   
3. Some sort of antigravity from the center pushes matter away from the central sun. If force increases the closer you get to the sun, exploration of it is impossible, and even aircraft will top out when the downward force matches lift. If it decreases, then artificial gravity is a better model.
   
4. There's an inner shell on which most creatures live ... which is essentially a planet with a ceiling.
   
5. Stick to classical mechanics: there's no gravity, and things slowly drift toward the central sun. Intertwined trees cover most of the surface (a little like Niven's Integral Trees), and humanity is used to being weightless. That may be a little too weird for what I have in mind.
   
6. Alien Space Bats.
   

Any other ideas?

[trechriron]

I personally would vote for Artificial Gravity plating at some healthy depth below the surface. There could be a whole labyrinth of tunnels, rooms and workings say half a mile below the surface. Everything from floating islands, pools of clean drinkable water, etc. come from the technology under the surface.

If the world has been left for eons, those tunnels, etc. could make for great adventures! Also, a planet-wide mass transit system in the tunnels that still works! Could be interesting...

[fmitchell]

I personally would vote for Artificial Gravity plating at some healthy depth below the surface. There could be a whole labyrinth of tunnels, rooms and workings say half a mile below the surface. Everything from floating islands, pools of clean drinkable water, etc. come from the technology under the surface.

If the world has been left for eons, those tunnels, etc. could make for great adventures! Also, a planet-wide mass transit system in the tunnels that still works! Could be interesting...

I'm swinging back toward centripetal force; my problem with artificial gravity is explaining why it doesn't work like natural gravity. Imagine a sphere, and then inside it a cylinder whose edges extend to the sphere's latitudes of 60 degrees. The residents perceive it as a flat or slightly convex surface that rises at the poles into icy "mountains". (The artificial sun isn't that warm; maybe most of the heat comes from the ground, and the sun is effectively a lamp.)

The official religious position is that digging through rock eventually reveals the impenetrable Edge of the World. I was thinking that at some point natural caves would give way to cylindrical tunnels bored into stone, and then the high-tech remains of the Builders and the outer surface. I like the idea of a transit system, and a hidden layer that keeps the ecosystem going.

[Razmus]

3. Some sort of antigravity from the center pushes matter away from the central sun. If force increases the closer you get to the sun, exploration of it is impossible, and even aircraft will top out when the downward force matches lift. If it decreases, then artificial gravity is a better model.

Actually, I'm rather enamored of that idea. The 'sun' isn't a big ball of hydrogen matter plasma -- it's an exotic contra-matter. Not anti-matter which still generates 'gravitons' and interacts with matter in predictable ways. Modern scientists still can't agree what exactly it is, but there is evidence that there is a sphere of energy created by the annihilation of very tiny amount of matter against this exotic material. Inside that sphere, there is apparently open 'portal/wormhole/tear in the dimensional fabric' where physics are different. Material there generates what we would consider anti-gravitons.

And yea... exploration there would be right out.

Well, unless the builders left behind some super-science suits/devices that could overcome the anti-gravitons, and protect people/things/etc from the annihilation.

[Skygalleons]

Since this is a Science Fantasy, my opinion is you are over thinking things. Just like most things in the Pulps are not possible, you don't think about it as that is just the way things are. I know there is a reluctance to use 'handwavium', but since you have a fantasy element to your setting, create a new fantasy element, one that defies the laws of our physics. After all, if magic works, I doubt if many players will care to much about the science part. THey will either like the setting or they won't.

[fmitchell]

The setting ties into the "Just Folks" setting I posted a while back: everyone thinks they live in a world of magic and gods, when it's all sufficiently advanced technology made by men. Exploring the central sun would disprove the dominant religion's belief that their god lives in the sun. Figuring out the physics of the place would prove men built it.

I suppose if I made alternate laws of nature that were still consistent, that would be good enough.

[Dimthar]

How close does this scenario will look compared to the first Era of Asimov's Foundation??

Are the Priests really knowledgeable scientists (Foundation) or just people who knows how to operate the technology left by the Ancients but do not understand it (Old Empire mechanics)??

For all I know you could have a Nano-Black Hole at the center, slowly devouring the inner parts of the world. The closer you are to the "core", time will move slower.

My 2 cents

Also it came to my mind the control the Gould Lords have over their worshipers (Stargate).

[fmitchell]

My thought is that even the priests don't really understand what's going on; their religion is grains of truth amidst a desert of supposition. (Yikes, did I write that?) The autonomic processes of the World have worked so well that its residents forgot it was a machine. The only breakdowns are in the AIs that run the world, who have become territorial and megalomaniacal, i.e. petty gods.

Which leads to the obvious plotline of the World breaking down ...

[Frobozz]

Centripetal force doesn't work for a Dyson sphere. At the equator, you have direct downwards force so it works there; 1g downwards. Everywhere else; getting worse as you climb in latitude, you have a sheer force that's trying to literally roll you along the ground toward the equator. The downward force gets less and the sheer force gets more. At 45deg north latitude, you have 1/2g downwards force, and 1/2g force pulling you south.

If you want the sci-fi route, you need antigraviational plating or an anti-gravity sun.

It's why Niven rings are far more feasible then Dyson spheres for stellar engineering concepts.

[Snuffy]

Perhaps make the people live at the "equator" with steep mountains to the sides that seem to reach to the skies. Strange things happen when people climb the mountains (dizziness, changes in gravitation) that have given to stories of folklore.

[ronpyatt]

Of course, some scientist found the answer to the riddle of including gravity among the known forces. Combing the Electromotive gravitational forces turned out to be quite a simple formula to apply to layered plates, which directs the field gravitons in a localized area. Later it was determined that those plates could pass on their properties through the veins of rocks by simply aligning the molecules (Polarizing) and "pointing" them the right direction to extend the field. The many combined repulsion veins hold the "sun" at the stable center of the sphere.

Or the "sun" could be the source of the anti-gravitational pulse that pushes at the sphere, where the closer you get to the sun, the heavier outward push one feels. Technically, making you heavier at the top of a mountain, but the effects may only be marginal.

[rabkala]

If you want a hollow world, just suspend reality and science! Come on man,these are fantasy realms! Don't think so hard.
Derr ... what we talk now?

[fmitchell]

Centripetal force doesn't work for a Dyson sphere.

That's why my current model is a cylinder inside a sphere; the sphere shields the inside from cosmic rays, and gravitic beams (or struts?) stabilize the false sun at the center. The cylinder provides a mostly flat surface to preserve apparent gravity until the "edge mountains" near each pole; to maximize area, it's approximately 1/sqrt(2) of the sphere's diameter, and 1/sqrt(2) of the diameter wide.

BTW, this isn't a Dyson sphere; the diameter is about the size of Earth, probably less. The sun isn't real, or at least it derives its power from artificial fusion.

I'm also wondering whether I can make the false sun a reflector that gathers sunlight from one or both poles. Recently I ran into a picture that's kind of close to what I had in mind. Alternately, perhaps light comes directly from the poles, making the equator nearly as cold as the Edge Mountains (which get almost no light).

[Snuffy]

Will there be a night time? Will the "sun" just shut off or will it gradually dim? There could be some fun scenarios when the sun starts malfunctioning turning on & off and the inhabitants have no idea what is going on.

[fmitchell]

Will there be a night time? Will the "sun" just shut off or will it gradually dim?

I was originally thinking the sun would rotate like a lighthouse; the dark side would present a "night sky" and a "moon" which really only makes sense to people raised on a conventional planet. (Another hint that the world is artificial.)

If I go with light from an external source, though, maybe it's a constant twilight (unless there's a rotating mirror). I'm avoiding a "long sun" from one pole to the other, because I never did read that Gene Wolfe series ... although maybe it would make the most sense: no gravitic beams or invisible struts, and the current residents of the Drum wouldn't know natural from unnatural.

P.S. I could also take Cyrus Reed Teed's solution: an inner cylinder that fills the sky, on which a false sky is projected.